Does friedewald formula underestimate the risk of ischemic heart disease?

Traditionally Friedewald formula has been used to calculate low density lipoprotein cholesterol (LDL-C) concentration though now direct homogenous methods for its measurement are also available. Clinical guidelines recommend the use of calculated LDL-C to guide therapy because the evidence base for cholesterol management is derived almost exclusively from trials that use calculated LDL, with direct measurement of LDL-C being reserved for those patients who are non fasting or with significant hypertriglyceridemia. In this study our aim was to compare calculated and direct LDL and their variation at different cholesterol and triglyceride levels. Fasting lipid profile estimation was done on 503 outpatients in a tertiary hospital. Both direct and calculated LDL were then compared. Mean fasting direct LDL was found to be higher than calculated LDL in 87.1 % of subjects by 8.64 ± 8.35 mg/dl. This difference was seen a all levels of cholesterol and triglyceride. Using 130 mg/dl LDL cholesterol as cut off fewer subjects were classified as high risk by calculated LDL than direct LDL. In conclusion, direct LDL is higher than calculated LDL. Compared with direct measurement, the Friedewald calculation underestimates the risk for ischemic heart disease.